1. Field of the Invention
The present invention relates to a runflat tire system, more particularly to a support ring disposed inside a pneumatic tire to support the backside of the tread of the deflated tire to increase the runflat distance.
2. Related Art
In recent years, a runflat tire system by which, even if the tire goes flat, it is possible to travel for a very long distance for example several hundred kilometers at a relatively high speed of up to about 80 km/hr has been proposed. Such techniques are disclosed in the Japanese patent application publication NOS. 8-504389 (WO 94/13498 A1), 10-6721 (U.S. Pat. No. 5,891,279 A) and 2001-354002 (U.S. Pat. No. 6,415,839 B1).
FIG. 11 shows an assembly of a pneumatic tire 2, wheel rim 3 and a support ring disclosed in the above-mentioned publications. In this assembly, even if the tire be punctured, it is possible to travel for a relatively long distance at usual speed. However, the steering stability in runflat mode is not so good. This is especially true when the tire goes flat during high speed running. Thus, there is room for improvement.
The inventors therefore, made a study on the correlation between the runflat steering stability and the parameters of the support ring, and found that the stability can be improved by: increasing the contact area of the support ring with the inside of the tire tread portion; increasing the lateral rigidity of the support ring; and increasing the torsional rigidity the support ring around the vertical axis. These must be achieved without increasing the weight of the support ring and without losing the radial rigidity and durability because these are the fundamental requirements of the support ring.
It is therefore, an object of the present invention to provide a support ring for a runflat tire system, by which the runflat steering stability can be improved, and thereby safe and long distance traveling is possible in runflat mode.